1. Field of the Invention
The present invention relates to a stroke bearing that can be used in devices performing repetitive relative motion such as industrial robots, office automation equipment and measuring instruments.
2. Description of the Prior Art
A known example of this type of stroke bearing is indicated in FIG. 1 and FIG. 2. As indicated in FIG. 1 and FIG. 2, this stroke bearing has ball and cage assembly 3 comprised by numerous rolling elements in the form of balls 1 arranged to rotate freely held by cage 2, and outer sleeve 4 and shaft 5 mutually engaged while allowed to slide and rotate freely by means of said ball and cage assembly 3. Furthermore, a device is suitably contrived that prevents said stroke bearing from coming out when installed in each of the above-mentioned apparatus so that ball and cage assembly 3 does not come out of outer sleeve 4 during this sliding.
In the stroke bearing having the above-mentioned constitution, for example, shaft 5 is moved back and forth or rotated with outer sleeve 4 being either fixed or movable. As a result, the apparatus in which said stroke bearing is incorporated performs smooth relative motion.
3. Problems that the Invention is to Solve
However, in the stroke bearing of the prior art, the degree of freedom of the relative operating states of the above-mentioned outer sleeve and shaft, since they are able to move freely in the axial and radial directions, is large. In the case of incorporating said stroke bearing in an apparatus such as a machine tool to operate in the manner of following, for example, a helical path of a moving part with respect to a stationary part, it is necessary to provide a separate guide mechanism to move said moving part along a helical path, thus resulting in the stroke bearing of the prior art having the disadvantage of leading to increased manufacturing costs for the apparatus. In addition, the stroke bearing of the prior art also has the disadvantage of having to separately provide a stopper device on the apparatus for preventing cage and ball assembly 3 from falling out.